Context
∙ Rotating black holes (a.k.a. Kerr black holes) have a unique feature: a region outside their outer event horizon called the ergosphere.
What is a Black Hole?
∙ A black hole is an extremely dense object whose gravity is so strong that nothing, not even light, can escape it.
∙ A black hole does not have a surface, like a planet or star. Instead, it is a region of space where matter has collapsed in on itself.
∙ This catastrophic collapse results in a huge amount of mass being concentrated in an incredibly small area.
∙ Formation: A black hole is formed when a really massive star runs out of fuel to fuse, blows up, leaving its core to implode under its weight to form a black hole.
∙ The centre of a black hole is a gravitational singularity, a point where the general theory of relativity breaks down, i.e. where its predictions don’t apply.
∙ A black hole’s great gravitational pull emerges as if from the singularity.
Rotating Black Hole
∙ A rotating black hole is also called a Kerr black hole.
∙ There are two event horizons, the outer and the inner.
∙ The region of space in-between the two horizons is the ergosphere.
∙ Anything inside the ergosphere will be dragged by the black hole and rotate with it but it can still escape.
∙ However, anything inside the inner event horizon can never escape.
∙ Scientific Significance: We can extract rotational energy from a rotating black hole.
∙ If something is sent inside of the ergosphere, and split it up into two parts, one goes in the black hole while the other comes out.
∙ The part coming out can be made to have a much higher speed, hence higher energy.
| Do You Know?– Known black holes fall into two classes: a. Stellar mass: 5 to tens of times the Sun’s mass; b. Supermassive: 100,000 to billions of times the Sun’s mass;c. Middleweight black holes may exist between these classes, but none have been found to date.– Spaghettification: As objects approach the event horizon of a black hole, they’re horizontally compressed and vertically stretched, like a noodle.– Sagittarius A*: Sagittarius A* is more than 25,000 light years from Earth – nearest supermassive black hole, with an estimated mass millions of times that of Sun. a. Often abbreviated by researchers to Sgr A* (pronounced “Sagittarius A star”), it sits in the constellation of Sagittarius at the heart of the Milky Way. |
